/**
 * M1 / x^2 == M2 / (L - x)^2
 */
#include <bits/stdc++.h>
using namespace std;

#include <bits/extc++.h>
using namespace __gnu_pbds;

using Real = long double;
using llt = long long;
using pii = pair<int, int>;
using vi = vector<int>;
using vvi = vector<vi>;

int main(){
#ifndef ONLINE_JUDGE
    freopen("z.txt", "r", stdin);
#endif
    ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(0);
    int nofkase = 1;
    // cin >> nofkase;
    while(nofkase--){
        int M1, M2, L, m;
        cin >> M1 >> M2 >> L >> m;
        Real ans = L / (1 + sqrt((M2 + 0.L) / M1));
        cout << fixed << setprecision(3) << ans << endl;
    }
    return 0;
}